The present invention relates generally to power generation equipment, and more particularly to improved heat exchangers for turbines.
Gas turbines and microturbines typically use heat exchangers, also known as recuperators, to increase their efficiency. In order to increase their efficiency, air-to-air primary surface or plate fin heat exchangers are typically used to recover thermal energy from high temperature exhaust gases emitted from such turbines. The heat exchanger typically comprises a hot-side flow path and a cold-side flow path. The high temperature exhaust gases of the turbine are typically routed through the hot-side flow path of the heat exchanger, while a relatively cooler combustion air exits a compressor and is routed through the cold-side flow path on its way to a combustor. Heat energy is typically transferred from the high temperature exhaust gases in the hot-side flow path to the lower temperature combustion air disposed in the cold-side flow path by convection from the high temperature exhaust fluid to a wall adjacent the cold-side flow path thereby heating the combustion air. As a result, the combustion air exits the heat exchanger and enters the combustor having been pre-heated and thereby providing increased cycle efficiency and utilizing the heat energy from the high temperature exhaust gases that would otherwise be lost.
While heat exchangers have demonstrated the potential for high efficiency in gas turbines and microturbines, some problems remain associated with the heat transfer between the high temperature exhaust gases and the combustion air. In some designs, the heat transfer between the high temperature exhaust gases and the combustion air primarily occurs between smooth channels formed between corrugated sheets thereby failing to optimize the surface area used in the conduction of heat between the gases and the air. The smooth channels typically have an undesired characteristic of providing low thermal transfer coefficients between the channel surface and the combustion air.
Accordingly, there is a need in the art for a turbine having an improved heat exchanger that provides improved heat transfer characteristics.